JP4575189B2 - Shield film for shielded flexible printed circuit board and shielded flexible printed circuit board using the same - Google Patents

Description

  The present invention relates to a shielded flexible printed wiring board used in devices such as computers, communication devices, and video cameras, and a shield film used therefor. In particular, the present invention relates to a shielded flexible printed wiring board that is excellent in electromagnetic wave shielding properties and that can effectively impart electromagnetic wave shielding characteristics to a flexible printed wiring board having a high wiring density, and a shield film used therefor.

  Flexible printed circuit boards (hereinafter referred to as “FPCs”) are frequently used to incorporate circuits in complex mechanisms in electronic devices such as mobile phones, video cameras, and notebook computers that are rapidly becoming smaller and more functional. ing. Furthermore, taking advantage of its excellent flexibility, it is also used for connection between a movable part such as a printer head and a control part. In these electronic devices, electromagnetic wave shielding measures are indispensable, and flexible printed wiring boards (hereinafter referred to as “shielded FPC”) with electromagnetic wave countermeasures are also used in FPCs used in the apparatus. I came.

7A and 7B are diagrams showing an example of this conventional shield FPC. FIG. 7A is a plan view, and FIG. 7B is an enlarged cross-sectional view taken along line BB in FIG. 7A.
In FIG. 7, the shield FPC 30 is obtained by bonding a base film 31 and a shield film 35. The base film 31 is obtained by sequentially providing a printed circuit 33 and an insulating film 34 on a base film 32. The shield film 35 has a cover layer 36 and a shield layer 37 provided on one surface thereof. The shield layer 37 includes a metal layer 37b or a metal layer 37b and a conductive adhesive layer 37a.

  The printed circuit 33 includes a plurality of conductive pattern lines such as a signal line 33a and a ground line 33b. The insulating film 34 of the base film 31 is provided with a notch 34a on a part of the ground line 33b of the printed circuit 33, and the upper surface 33c of the ground line 33b is exposed. When the shield film 35 is bonded, the conductive adhesive 37a is filled in the notch 34a of the insulating film 34 and comes into contact with the upper surface 33c of the ground line 33b, so that the shield layer 37 of the shield film is connected to the ground line 33b. And will be grounded.

In this way, the ground wire 33b and the shield layer 37 of the shield film are connected to each other, thereby being grounded and functioning as an effective electromagnetic wave shield layer.
In recent years, a further increase in wiring density has been required, and there is an urgent need to reduce the width of the ground line 33b. On the other hand, with the increase in the speed of electronic devices, a shield structure with higher electromagnetic shielding properties is required. That is, there is a demand for strengthening the ground while being restricted by the ground wire that can be grounded by downsizing and high density.

The present invention has been made to meet the above-mentioned demands, and provides a shielded FPC that is excellent in electromagnetic shielding properties and that can effectively shield electromagnetic waves even against an FPC having a high wiring density. It is an object to provide a shield film that can be provided.
For example, the present inventors have focused on strengthening grounding by connecting a ground wire and a shield layer of the housing and the shield FPC after the shield FPC is accommodated in the housing.

Means and effects for solving the problems

The shield film of the present invention is a shield film of a shield FPC having a base film in which a printed circuit and an insulating film are sequentially provided on a base film, and a shield film covering at least one surface of the base film.
The shield FPC of the present invention is a shield FPC using the above-described shield film of the present invention.
And in order to achieve the said subject, this invention has mainly the following some characteristics. In the present invention, the following main features are provided singly or appropriately combined.

  The shield film of the present invention is provided with an adhesive layer, a metal layer, and a cover layer in order, and the shield layer is formed by adhering the adhesive layer to the printed circuit side of the base film.

The cover layer is a conductive resin layer or an anisotropic conductive resin having a desired conductivity under a predetermined condition at least in the thickness direction and having no conductivity in a direction (plane direction) perpendicular to the thickness direction. Is a layer.
In the case of the anisotropic conductive resin layer, specifically, the anisotropic conductive resin layer (hereinafter referred to as “a”) that is left in the layered state and has conductivity in the thickness direction but no conductivity in the plane direction. If it is necessary to do so, it is referred to as “A-type anisotropic conductive resin layer”), b) In the laminated state, there is no conductivity in the thickness direction or in the surface direction, but the thickness direction under a predetermined condition An anisotropic conductive resin layer (hereinafter referred to as “B-type anisotropic conductive resin layer” when it is necessary to distinguish) is included.

  In this cover layer, “desired conductivity” means that the ground layer necessary for the shield layer under the cover layer to exhibit the electromagnetic wave shielding function when the surface portion at the desired position is connected to the ground member in the vicinity thereof. The conductivity to the member.

The adhesive layer of the shield film is preferably a conductive adhesive layer or an anisotropic conductive adhesive layer. However, when a ground line cannot be provided on a printed circuit, a non-conductive adhesive is used. It can be a layer.
Furthermore, since the function of the electromagnetic wave shield is caused by a grounded conductor surface, in this specification, the shield layer is a metal layer when the adhesive layer is a conductive adhesive layer having conductivity in the surface direction. The conductive adhesive layer is also referred to, and in other cases, only the metal layer is meant.

According to the shield film having the above-described configuration and the shield FPC using the shield film, the cover layer is not only a conductive resin layer and an A-type anisotropic conductive resin layer, but also a B-type anisotropic conductive resin layer. Also in this case, under predetermined conditions, it becomes conductive at least in the thickness direction, so that it is electrically connected at any position on the surface of the shield layer and the cover layer. As a result, when the surface of the desired position of the cover layer is connected to a ground member in the vicinity thereof, the shield layer is grounded. Therefore, the adhesive layer of the shield film may be non-conductive.

  In addition, in the case where the cover layer is a B-type anisotropic conductive resin layer, the surface portion of the selected desired position of the cover layer and its surroundings are not substantially electrically conductive. Even if the surface portion of the selected desired position is connected to another member having a predetermined potential, the entire cover layer does not become the predetermined potential. Therefore, the surface portion of the selected desired position of the cover layer and its surface Electrical independence from the surroundings is maintained.

In addition, when the adhesive layer of the shield film is composed of a conductive adhesive layer or an anisotropic conductive adhesive layer, and the predetermined pattern line of the printed circuit connected to the metal layer through them is a ground line, By connecting the surface portion of a desired position of the cover layer to the ground member, the grounding of the ground line is further strengthened.
Further, in the case of an FPC having a high density wiring, when a ground wire is not provided as described above and a non-conductive adhesive is used, as described above, the surface portion of a desired position of the cover layer is located in the vicinity thereof. An effective shield can be obtained simply by connecting to the ground member.
Note that the “ground member in the vicinity thereof” means, for example, a portion that is at a ground potential such as a housing of a device in which the shield FPC is used.

As described above, according to the shield film of the present invention and the shield FPC using the shield film, the grounding of the shield layer only connects the surface portion of the cover layer arbitrarily selected at the desired position to the ground member in the vicinity thereof. Therefore, it is not necessary to provide a wide ground line as a part of the printed circuit, and the wiring density of the signal lines can be increased accordingly.
Further, for example, a ground member such as a housing of a device in which the shield FPC is used can have a larger area than a ground line in a conventional printed circuit, and without passing through another ground circuit. Since it is directly connected to a nearby ground member, the ground impedance is small, and therefore the electromagnetic wave shielding effect of the shield layer is also large.

Moreover, in order to maintain the electrical independence of a desired portion on the surface of the cover layer, it is preferable that the anisotropic conductive resin layer is composed of a B-type anisotropic conductive resin layer.
According to the shield film having the above-described configuration and the shield FPC using the shield film, the cover layer is anisotropically conductive resin whose resistance is reduced when the pressure is applied in the thickness direction, the conductivity is improved, and the electrical conductivity is improved. Since it is a layer, it is electrically connected to the shield layer at a desired position on the surface of the cover layer simply by pressing or heating / pressing the surface portion of the cover layer at a desired position. You can select and connect. In addition, since there is no conductivity in the thickness direction in the portion not under pressure or the like, the insulation from the desired position under the pressure or the like is maintained, and the electrical independence is maintained. .

  In particular, when the predetermined pattern line of the printed circuit connected to the shield layer is a ground line, the surface portion of the cover layer at a desired position where the pressure is applied is connected to the ground member. The grounding of the ground line can be strengthened.

In addition, in the shield film of the present invention, it is preferable that an electrode is provided on the surface portion of a desired position of the cover film so that it can be connected to a nearby ground member or the like.
According to the shield film having the above-described configuration and the shield FPC using the shield film, the electrode ensures energization with a predetermined pattern line of the printed circuit connected to the shield layer.

  In particular, if the predetermined pattern line of the printed circuit is a ground line, the shield FPC can be reliably and easily grounded simply by connecting the electrode portion of the cover film to a ground member in the vicinity thereof. .

The first embodiment of the present invention will be described below based on the drawings.
FIG. 1 is an explanatory view of a shield FPC according to the present embodiment, a partially cutaway plan view, and FIG. 2 is an AA enlarged sectional view of FIG.

In FIG. 2, a shield FPC 10 is obtained by bonding a base film 1 and a shield film 5.
The base film 1 includes a base film 2, a printed circuit 3 on the base film 2, and an insulating film 4 that covers the printed circuit 3 on the base film 2. The printed circuit 3 includes a plurality of conductive pattern lines such as a signal line 3a and a ground line 3b.
The shield film 5 covers at least one surface of the base film 1. In FIG. 2, one surface on the insulating film 4 side is covered.

  The shield film 5 includes a shield layer 7 that covers the base film 1 and a cover layer 6 that further covers the shield layer. A part of the shield layer 7 is connected to a predetermined pattern line of the printed circuit 3. In FIG. 2, the predetermined pattern line is a ground line 3b, and the shield layer 7 is connected to the ground line 3b.

  The insulating film 4 of the base film 1 is provided with a notch 4a on a part of the ground line 3b of the printed circuit 3, and the upper surface 3c of the ground line 3b is exposed. When the shield film 5 is bonded, the conductive adhesive 7a is filled in the cutout portion 4a of the insulating film 4 and comes into contact with the upper surface 3c of the ground wire 3b, so that the shield layer 7 of the shield film 5 is connected to the ground wire 3b. Connected.

The shield layer 7 includes a metal layer 7 b and a conductive adhesive layer 7 a that adheres the metal layer 7 b to the base film 1. The metal layer 7b includes a thin film or a metal foil formed by a vapor deposition method or a sputtering method.
In order to allow the cover layer 6 to be directly attached to the shield layer 7, it is preferable that the cover layer 6 has adhesiveness or tackiness.
The cover layer 6 basically includes a film-like resin layer 6a and a plurality of conductive particles 6b. The plurality of conductive particles 6b are substantially uniformly diffused in the film resin layer 6a.

The film-like resin layer 6a has a thickness in the range of about 1 μm to about 50 μm, and each conductive particle 6b has a diameter in the range of about 1 μm to about 100 μm. The cover layer 6 is a conductive resin layer, or each of the conductive particles 6b is partially exposed from the film resin layer 6a, and has an A-type anisotropic having conductivity in at least the thickness direction without applying pressure. It is a conductive resin layer.
Proportion of the conductive particles 6b are included in the film-like resin layer 6a, when the film-like resin layer 6a was 100 parts by weight, the proportion in the range of about 1 part by weight to about 300 parts by weight. If the anisotropic conductive resin, the proportion of the conductive particles 6b included in the film-like resin layer 6a is film-like resin layer 6a is taken as 100 parts by weight, from about 1 parts to about 30 parts by weight Preferably, the proportion is in the range of about 5 parts by weight to about 20 parts by weight.

According to the arrangement of the shield film 5, and the shield FPC10 using the same, the cover layer 6 is conductive in the plane direction in the thickness direction there Ru conductive resin layer, or the thickness direction conductivity However, since it is an A-type anisotropic conductive resin layer that is not electrically conductive in the plane direction, it does not conduct to the shield layer 7 at any position on its surface without applying pressure to the cover layer 6. Then, it can be connected to the ground member at a desired position. When the shield layer is electrically connected to the ground line 3b of the printed circuit 3, the ground of the shield FPC 10 can be strengthened by connecting the surface of the cover layer 6 to a ground member.

Next, a second embodiment will be described based on FIG.
The plan view of the shield FPC of the second embodiment is the same as that of FIG. 1, and FIG. 3 is an AA enlarged sectional view of the second embodiment of FIG. 3 differs from the first embodiment of FIG. 2 in that each conductive particle 6b of the cover layer 6 is completely embedded in the film resin layer 6a, and the desired position of the cover layer 6 is different. surface portion 8 is predetermined condition, for example, or pressurized above a predetermined pressure is that it have the desired conductivity in the thickness direction is recessed slightly by heating and pressing at a given temperature and pressure.
Further, since the surface portion 8 at the desired position and its surroundings are not electrically conductive, the surface portion 8 at the desired position selected on the cover layer 6 can be connected to another member having a predetermined potential. The entire cover layer 6 is not at the predetermined potential. In other words, the electrical independence between the surface portion 8 of the selected desired position of the cover layer 6 and its periphery is maintained.

When the predetermined pattern line of the printed circuit 3 connected to the shield layer 7 is the ground line 3b, the surface portion 8 at a desired position of the cover layer 6 is connected to a ground member in the vicinity thereof, thereby shielding The grounding of the FPC ground line can be further strengthened.
The “ground member in the vicinity thereof” refers to a portion at a ground potential such as a housing of a device in which the shield FPC is used.

In the shield film 5 of the first and second embodiments, it is preferable that an electrode 9 is provided on the surface portion 8 at a desired position of the cover layer 6. The electrode 9 is preferably a metal foil in consideration of the thickness of the shield film 5 and the shield FPC 10 when flexibility is required. When the reinforcing effect of the shield film 5 or the like is required, the electrode is preferably a metal plate.
According to the shield film 5 having the above configuration and the shield FPCs 10 and 20 using the shield film 5, the shield layer 7 is connected to the electrode 9 through the cover layer, so that the electrode 9 is connected to the ground member. By doing so, the shield layer 7 is reliably grounded.

  In the first and second embodiments, the adhesive layer of the shield film 5 is a conductive or anisotropic conductive adhesive layer, but may be a nonconductive adhesive layer. In that case, the printed circuit cannot be electrically connected to the metal layer 7b through the resin layer even if there is a ground line, but the metal layer 7b is connected to a nearby ground member through the electrode 9 provided on the cover layer 6. Surely grounded.

The thickness of each layer of the shield film 5 of the shield FPCs 10 and 20 is as follows.
Layer composed of conductive adhesive layer 7a about 5-30 μm
Layer composed of metal layer 7b, about 0.05 to 35 μm
Cover layer about 1-50μm

Test example 1

Next, a characteristic test example of the B-type anisotropic conductive resin layer (hereinafter simply referred to as “anisotropic conductive resin layer”) will be described with reference to FIG.
First, as Test Example 1, with respect to the B-type anisotropic conductive resin layer constituting the cover layer 6, a change in resistance with respect to the thickness T of the anisotropic conductive resin layer under a certain load was measured.
In FIG. 4, reference numeral 11 denotes a B-type anisotropic conductive resin layer, 12 denotes a metal layer, 13a and 13b denote two electrode terminals that serve as loads, and 14 denotes a resistance measuring device.
An anisotropic conductive resin layer 11 is adhered on the metal layer 12. The electrode terminals 13a and 13b are connected to current input / output terminals of the resistance measuring device 14, respectively.

The anisotropic conductive resin layer 11 is obtained by diffusing and arranging conductive particles approximately 5% by weight on an epoxy resin layer. T indicates the thickness of the anisotropic conductive resin layer 11. The conductive particles are Cu powder (dendritic powder) coated with Ag. The average particle size is about 20 μm.
A Cu foil is used as the metal layer 12.
The electrode terminals 13a and 13b are square pillars each having a square bottom surface of L × Lmm ² . Both electrode terminals 13a, 13b are separated by a distance L. Here, L is about 10 mm.
The surface of the anisotropic conductive resin layer 11 is pressed in the thickness direction of the anisotropic conductive resin layer 11 with a predetermined load W by the electrode terminals 13a and 13b. Then, the resistance of the anisotropic conductive resin layer 11 is measured.

  The results are shown as a graph in Table 1 and FIG. In any case, it is understood that when pressure is applied, the resistance decreases and the electrical continuity is improved.

Test example 2

Test example 2 will be described with reference to FIG.
With respect to the anisotropic conductive resin layer constituting the cover layer 6, the resistance before and after heating and pressurizing at a predetermined temperature and pressure was measured for each thickness T ₀ .
FIG. 6A shows before heating / pressing, and FIG. 6B shows after heating / pressing. 6A and 6B, reference numeral 14 denotes a resistance measuring device, 15a and 15b denote first and second metal layers serving as electrodes, and 16 denotes an anisotropic conductive resin layer.
An anisotropic conductive resin layer 16 is adhered on the first metal layer 15a. The first and second metal layers 15a and 15b are connected to current input / output terminals of the resistance measuring device 14, respectively. An anisotropic conductive resin layer 16 is sandwiched between the first and second metal layers 15a and 15b. Then, the resistance of the anisotropic conductive resin layer 16 before and after heating and pressing is measured.

The anisotropic conductive resin layer 16 is obtained by diffusing and arranging conductive particles approximately 5% by weight in an epoxy layer. T ₀ indicates the thickness of the anisotropic conductive resin layer 16 before heating and pressing. T ₁ indicates the thickness of the anisotropic conductive resin layer 16 after heating and pressing.
The conductive particles are balls plated with Au. Its average particle size is about 4.6 μm.
Cu foil is used as the first and second metal layers 15a and 15b.
The anisotropic conductive resin layer 16 is heated and pressurized in the thickness direction of the anisotropic conductive resin layer 16 in a state where a predetermined temperature and a load W are applied. Here, the second metal layer 15b is bonded to the anisotropic conductive resin layer 16 by applying pressure at 160 ° C. and 20 kgf / cm ² for 30 minutes. The thickness T ₁ of the anisotropic conductive resin layer 16 after heating / pressing is smaller than the thickness T ₀ before heating / pressing. Then, the resistance of the anisotropic conductive resin layer 11 is measured.

The results are shown in Table 2. The resistance (mΩ) before and after heating and pressing is shown for each thickness T ₀ before heating and pressing.
In any case, it is understood that when pressure is applied, the resistance decreases and the electrical continuity is improved.

As can be seen from Test Example 1 and Test Example 2, the B-type anisotropic conductive resin layer can obtain desired conductivity in the thickness direction under predetermined conditions (pressurization or heating / pressurization), and in the surface direction. There is no conductivity.
Therefore, according to the shield film 20 using this as the cover layer 6 and the shield FPC 20 using the same, it is possible to easily perform grounding simply by connecting the surface portion of a desired position of the cover layer to the ground member in the vicinity thereof. In addition, electrical independence from other parts is maintained.

It is explanatory drawing of the shield flexible printed wiring board of 1st Embodiment, and is a partially notched top view. AA expanded sectional view of Drawing 1 showing a 1st embodiment. Other AA expanded sectional views of Drawing 1 showing a 2nd embodiment. The figure which shows the outline of the apparatus of Test Example 1 Graph showing the results of Test Example 1 The figure which shows the outline of the apparatus of Test Example 2 Explanatory drawing of conventional shield flexible printed wiring board

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base film 2 Base film 3 Printed circuit 3b Predetermined pattern line 4 Insulating film 5 Shield film 6 Cover layer 7 Shield layer 7b Metal layer 7a Conductive adhesive layer 9 Electrode 10 Shield flexible printed wiring board (1st Embodiment)
20 Shield flexible printed wiring board (second embodiment)

Claims (6)

A base film in which a printed circuit and an insulating film are sequentially provided on a base film;
A shield flexible printed wiring board shield film having a shield film covering at least one side of the base film,
The shield film has a metal layer, an adhesive layer that adheres the metal layer to the base film, and a cover layer that covers the metal layer,
The cover layer is
Has a film-like resin layer and said film-like resin layer plurality of conductive diffused disposed evenly in the particle,
Each of the conductive particles is partially exposed from the film resin layer, or the conductive particles are partially exposed from the film resin layer under predetermined conditions, and at least the thickness direction of the exposed position is desired. A shield film for a shielded flexible printed wiring board, wherein the shield film is an anisotropic conductive resin layer having the above conductivity.   The cover layer has a desired conductivity in the thickness direction at the position of the surface portion under a condition in which an electrode provided on the surface portion at a desired position is pressurized at a predetermined pressure or higher. 2. The shield film for a shielded flexible printed wiring board according to claim 1, wherein the shield film is an anisotropic conductive resin layer having no conductivity in a direction perpendicular to the direction.   The shield film for a shielded flexible printed wiring board according to claim 1, wherein the adhesive layer is an adhesive layer having conductivity at least in the thickness direction. A base film in which a printed circuit and an insulating film are sequentially provided on a base film;
A shielded flexible printed wiring board having a shield film covering at least one side of the base film,
The shield film has a metal layer, an adhesive layer that adheres the metal layer to the base film, and a cover layer that covers the metal layer,
The cover layer is
Has a film-like resin layer and said film-like resin layer plurality of conductive diffused disposed evenly in the particle,
Each of the conductive particles is partially exposed from the film resin layer, or the conductive particles are partially exposed from the film resin layer under predetermined conditions, and at least the thickness direction of the exposed position is desired. A shielded flexible printed wiring board characterized by being an anisotropic conductive resin layer having the conductivity of   The cover layer has a desired conductivity in the thickness direction at the position of the surface portion under a condition in which an electrode provided on the surface portion at a desired position is pressurized at a predetermined pressure or higher. The shielded flexible printed wiring board according to claim 4, wherein the shielded flexible printed wiring board is an anisotropic conductive resin layer having no conductivity in a direction perpendicular to the direction.   The adhesive layer of the shield film is a conductive adhesive layer or an anisotropic conductive adhesive layer, and is connected to a ground line of a printed circuit of the base film. Shield flexible printed wiring board.

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